Help with Toyota brakes please

Double_Down

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So I have a 1992 Toyota 4wd. I'm curently running 33x10.5 tires on it. I have stainless lines all the way around, EBC pads in front, stock type pads in the rear drums, new slave cylinders in the rear drums. I've bled and re-bled the brakes so many times I can't keep track. I made a bracket with a rod end for the rear LPV, as I disconnected the LPV from the axle when I put longer springs in. When the rod of the LPV is adjust all the way up, the rear brakes lock up before the front, and the braking perfomance is poor. When the rod is adjusted down (say past horizontal), the rear doesn't lock up first, but I still have poor breaking performance. I can't get the front brakes to lock up, and the pedal feel is soft. Also, when the rod is adjusted down, I get strange behavior in the front brakes when they are released. If I release the pedal quickly, I feel a delay, and then a pop like the brakes release. If I release the pedal slowly, I don't hear/feel the pop. When the LPV rod is the full up position I do not get this strange behavior.

Having 4 piston calipers and knowing people have raced with these brakes with success, makes me wonder what I am missing. Should I replace the LPV with a manual front to rear bias valve? Should I replace the master cylinder (I have about 100k on this one)? Is there a way to test if the master cylinder is bad? Do I need a bigger master cylinder to get more pressure and better feel?

My goals are to have a stiffer pedal with better feel, and better stopping performance. I am open to any and all ideas, and do not mind re-addressing any of the points mentioned above in case I missed something. Thanks for your help all.
 

Wayside

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When the rod of the LPV is adjust all the way up, the rear brakes lock up before the front
This is normal because the rod is telling the valve that you have a load in the bed of the truck allowing more pressure to get to the rear brakes. That is why the rears are locking up when rod is up.

Now the rod is adjusted down the rears should not lock up. The rod is telling the valve that there is no load in the bed allowing less pressure to get to the rear brakes.

As for the soft pedal could be a few things are you rear brakes up in adjustment? Or the master is bad. When you get the popping in the pedal, I am wondering if you are getting LPV to close fully and it sticking upon quick release of the pedal. Also how hard and how fast are you jumping on the pedal to get this to happen?

As for changing the master this is a double side blade. If you go to a smaller master cylinder bore diameter you will gain more pressure but lose the volume. Basically you will have to pump the pedal a few times to stop the truck but it will stop on a dime. On the other hand if you go to a bigger master cylinder bore diameter you will gain volume but will lose pressure which would mean a nice high pedal but you would need two feet plus a boat anchor to stop the truck. When you change the master in the name a better braking performance its all about finding that happy medium. As for the braking performance at the wheels, bigger is better. But if you change one thing from stock on a braking system you affect a lot of things.

Also I don't know if this theory hold true or not but this is what we learned in school. Coefficient of friction (COF) of the brake pads and shoes is basically how grabby the are. A lower COF lets say .4:1 will last longer but will have less grab. A higher COF (.6:1) will grab more but won't last as long.

I hope this helps a little
 

California MiniTruck

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I have plenty of used proportion valves here if you want to try and change it out. I have seen these go out many times and I sell them for about $45 and I give a 100 day warranty with the product. Let me know if there is anything else you need for your Toyota truck, we specialize in Toyota and Nissan Trucks:D:D:D
 

California MiniTruck

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Yea I was going to say what Matt said but I was not sure what the truck was used for. I ran a hard line on my 92 Toy pu right back to the breaks, that thing would lock up all the 31" tires and stop on a dime. Best thing to do unless its a daily drive, you dont want to lock up all 4 on the freeway!:D:D:D
 

Double_Down

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This is normal because the rod is telling the valve that you have a load in the bed of the truck allowing more pressure to get to the rear brakes. That is why the rears are locking up when rod is up.

Now the rod is adjusted down the rears should not lock up. The rod is telling the valve that there is no load in the bed allowing less pressure to get to the rear brakes.

As for the soft pedal could be a few things are you rear brakes up in adjustment? Or the master is bad. When you get the popping in the pedal, I am wondering if you are getting LPV to close fully and it sticking upon quick release of the pedal. Also how hard and how fast are you jumping on the pedal to get this to happen?

As for changing the master this is a double side blade. If you go to a smaller master cylinder bore diameter you will gain more pressure but lose the volume. Basically you will have to pump the pedal a few times to stop the truck but it will stop on a dime. On the other hand if you go to a bigger master cylinder bore diameter you will gain volume but will lose pressure which would mean a nice high pedal but you would need two feet plus a boat anchor to stop the truck. When you change the master in the name a better braking performance its all about finding that happy medium. As for the braking performance at the wheels, bigger is better. But if you change one thing from stock on a braking system you affect a lot of things.

Also I don't know if this theory hold true or not but this is what we learned in school. Coefficient of friction (COF) of the brake pads and shoes is basically how grabby the are. A lower COF lets say .4:1 will last longer but will have less grab. A higher COF (.6:1) will grab more but won't last as long.

I hope this helps a little
Very much so!

From what I have experienced and you describe the LPV seems to be working correctly, as I adjust it through it's range of motion.

The rear brakes have been adjusted (broke out the brake spoon to do it, don't really trust that self adjusting brake in reverse stuff to adjust the drums). When I get the popping I am not jumping on the pedal very hard. I am exerting a a straight consistent pressure in a effort to get the truck to stop quickly. I definitely don't feel I'm jumping on it. And again, I'm getting the popping feeling on release, like something is sticking. Either the front calipers or the LPV. I feel/hear the pop through the chassis, and don't really feel it through the pedal. No back pressure or anything of note in the pedal itself.

Correct me if I am wrong but if the master is bad, would the pedal eventually sink to the floor when I'm pushing on it? There is room between the pedal and the floor, and there is definitely a set amount of travel in it. Just when I get to the bottom of that travel, I feel that the brakes should be grasping harder, and preferably, locking up.


throw the LSPV in the trash and just run one hard line from the master to the rear.
Cool for a daily driver, or not so much?

Yea I was going to say what Matt said but I was not sure what the truck was used for. I ran a hard line on my 92 Toy pu right back to the breaks, that thing would lock up all the 31" tires and stop on a dime. Best thing to do unless its a daily drive, you dont want to lock up all 4 on the freeway!:D:D:D
So I take that as a no. This truck sees plenty of pavement time, so if I wanted to run a line directly from the master to the rear brakes, should I put an adjustable bias valve in between the front and rear?

Thanks to all for your help. This is a safety issue I'm eager to get sorted out. At least I have some things to try.
 

California MiniTruck

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Very much so!

From what I have experienced and you describe the LPV seems to be working correctly, as I adjust it through it's range of motion.

The rear brakes have been adjusted (broke out the brake spoon to do it, don't really trust that self adjusting brake in reverse stuff to adjust the drums). When I get the popping I am not jumping on the pedal very hard. I am exerting a a straight consistent pressure in a effort to get the truck to stop quickly. I definitely don't feel I'm jumping on it. And again, I'm getting the popping feeling on release, like something is sticking. Either the front calipers or the LPV. I feel/hear the pop through the chassis, and don't really feel it through the pedal. No back pressure or anything of note in the pedal itself.

Correct me if I am wrong but if the master is bad, would the pedal eventually sink to the floor when I'm pushing on it? There is room between the pedal and the floor, and there is definitely a set amount of travel in it. Just when I get to the bottom of that travel, I feel that the brakes should be grasping harder, and preferably, locking up.




Cool for a daily driver, or not so much?



So I take that as a no. This truck sees plenty of pavement time, so if I wanted to run a line directly from the master to the rear brakes, should I put an adjustable bias valve in between the front and rear?

Thanks to all for your help. This is a safety issue I'm eager to get sorted out. At least I have some things to try.

Yea if your on the street I would most def put a adjustable valve on the rear. When you or if you eliminate the LPV it will make a major difference on your breaking power, just be careful on the street :)
 

matt_helton

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i had 2 trucks with no lspv........one was street/dirt and the other was my race truck but it also saw some street time too. lol.......anyways, one truck was a 2wd chassis with an 8" rear end and 32" tires........stopped awesome on the street.....no locking up issues in the rear..............my race truck was a 4wd chassis with a 9" in the rear with drum brakes on 35" tires.........it also has zero braking issues on dirt OR street. thats why i say ditch it and never look back. i never saw the need for an adjustable proportioning valve.
 

baja B-rad

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That valve is worthless. I just took the bar out that connects it to the axle. Dirt, street, I never have any problems. If you hit them hard enough you will damn near go through the window.

A while back mine was also making that popping noise and it had a soft petal. I replaced it with a new master and I havent had a problem since.
 

Double_Down

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Thought I would post an update. Based on the recommendations posted here, last night I put in a new master cylinder, and also removed the LPV from the rear. I kinda broke a cardinal rule of troubleshooting in that I changed two things at the same time. Anyway, the popping and *some* of the soft pedal went away. The rear is still locking up long before the front is though. While I would prefer a higher pedal with less travel (better feel) I guess that one is what it is. I'm going to get a Wilwood proportioning valve to play around with, and see if I can get the rear dialed in a little bit more.
 

Double_Down

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Does anyone know where to get a 1/8-27 NPT male to 10mmx1.0 female adapter? I'm hoping to use adapters as I go through these testing evolutions and not have to butcher up the brake lines or fittings. I'm hoping to find them online and place an order. It's difficult for me to get calls out during business hours.

I've checked Summit and Jegs. I also tried Crown for some fittings a while ago, but haven't gotten a response to my e-mail.

Thanks.
 

jrtorres

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This may seem obvious but keep in mind that the back of these toyota pickups weighs nothing...so the rear locking up may have something to do with that...the soft pedal in the front is something i'm also having an issue with at the moment haha.
 

Wayside

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Napa might have the adapter. As for the pedal you might want to try adjusting the rod inside the master or on the boster so there is less clearance, basicly so you can get more fluid in there. can't remember if the rod is in the master or on the boster on that truck.
 
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